Most beverage cans presently produced in the United States are so-called "two-piece cans" which are typically made from aluminum. A two-piece can includes a can body which has a cylindrical side wall portion and an integrally formed bottom wall portion. The can body is open at the top, terminating in an annular peripheral flange portion. The second component of a two-piece can is a can "lid" or "closure" which is more commonly referred to in the industry as a can "end." The can end has an annular peripheral flange or "curl" portion which is seamed to a corresponding peripheral flange portion of the can body to seal the opening in the can body. The can end is seamed to the can body after the can body has been filled with the desired beverage. Can ends are typically formed in a series of die presses which initially form the basic can end configuration or "shell." Subsequently. the shell has various operations performed thereon, such as embossing, debossing, scoring, rivet formation and tab staking, to complete the end. A can end press is described in U.S. Pat. No. 4,939,665 to Gold et al., issued Jul. 3, 1990, which is hereby incorporated by reference for all that it discloses.
Most can ends used in the packaging of pressurized beverages, such as soft drinks and beer, include a score panel. The score panel may be formed by a pair of closely spaced score lines which are provided in a generally ring-shaped configuration referred to herein as a "score profile." In one popular type of can end, the beginning portion and end portion of the score profile are spaced apart. This spaced apart region does not rupture during opening of the score panel and acts to retain the score panel on the can end after the primary score line has been ruptured. In this type can end, a separately formed tab member has an intermediate portion thereof riveted to a central portion of the can end at a position on the can end adjacent to the score panel. The tab member has a first end portion, generally referred to as a nose, which is initially positioned in contact with the score panel. The tab member has an opposite end portion which is generally formed in a ring-shaped configuration. In opening the can end, a user grasps the ring portion of the tab member and pulls upwardly, causing the tab member to pivot about an axis which is typically adjacent to the rivet on the tab nose end side of the rivet. Thus, pulling upon on the ring end portion causes the nose end portion to be urged against the score panel, causing the score panel to rupture and eventually to pivotally deflect about an axis defined generally by the gap between the beginning and end portions of the score profile. The following U.S. patents disclose various can end configurations and are hereby incorporated by reference for all that is disclosed therein: U.S. Pat. No. Des. 364,807, issued Dec. 5, 1995, to Taylor; U.S. Pat. No. Des. 265,463, issued May 1982 to Hasegawa; U.S. Pat. No. Des.-267,393, issued December 1982 to Gruodis et al.; U.S. Pat. No. Des.-275,373, issued September 1984 to Brown et al.; U.S. Pat. No. 3,259,265, issued July 1966 to Stuart; U.S. Pat. No. 3,291,336, issued December 1966 to Fraze; U.S. Pat. No. 3,424,337, issued January 1969 to Von Stocker; U.S. Pat. No. 4,205,760, issued June 1980 to Hasegawa; U.S. Pat. No. 4,210,257, issued July 1980 to Radtke; U.S. Pat. No. 4,465,204, issued August 1984 to Kaminski et al.; U.S. Pat. No. Des.-246,229, issued November 1977 to Saunders; U.S. Pat. No. Des.-250,933, issued January 1979 to Saunders; U.S. Pat. No. Des.262,517, issued January 1982 to Hayes; U.S. Pat. No. 4,175,670, issued November 1979 to Reynolds et al; U.S. Pa. No. 4,266,685, issued May 1981 to Lee. Jr.; U.S. Pat. No. 4,313,545, issued February 1982 to Maeda; U.S. Pat. No. 4,318,489, issued March 1982 to Snyder et al.; U.S. Pat. No. 4,733,793, issued Mar. 29, 1988, to Moen et al.; and U.S. Pat. No. 4,804,104, issued Feb. 14, 1988, to Moen et al.; and U.S. application Ser. No. 08/276,331, filed Jul. 15, 1994, for "SCORE LINE GROOVE FOR CONTAINER END MEMBERS" by Sedgeley; and No. 08/393,140, filed Feb. 21, 1995, for "SCORE LINE GROOVE FOR CONTAINER END MEMBERS" by Sedgeley.
Score panel design requires a careful balancing of design parameters. If a designer selects a score line depth which is too deep, the resulting can ends are subject to being ruptured during production and during packaging and shipping operations. On the other hand, if the score depth is too shallow, excessive force may be required to rupture the score. In such a situation, even if the user is physically able to apply sufficient force to rupture the score line, the tab and the score panel itself may deform in a manner to prevent complete rupture of the full length of the score. The tendency of a score panel to deform excessively during score rupture is, to a large extent, a function of the relative stiffness of the score panel. The stiffness of a score panel may, in turn, be influenced by the metal gauge, i.e., the thickness of the score panel, and also the amount of "slack" metal in the score panel. Score panel slack may be produced by various sources, including rivet formation and also the very scoring needed to create a score panel. The relative size of a score panel also affects the rupture performance of a score panel since a panel of larger area tends to bend more and, thus, diffuse the rupture force applied by the tab member more than a smaller score panel of the same metal gauge.
One common technique used for increasing the relative stiffness of a score panel is to create a deboss panel which circumscribes the score panel and rivet. Another technique is to form a raised or "embossed" metal bead in the middle of the score panel to take up metal slack.